1. Field of the Invention
This invention relates to a cutting chain (saw chain) for cutting aggregate materials and more particularly to a cutting chain having guard links with guard portions that precede the cutting links and permit efficient cutting while protecting the leading edge of the cutting links.
2. Background Information
Cutting chains are commonly used to cut trees and logs and more recently have been successfully applied to the cutting of aggregate materials such as masonry, stone and the like. However, there is a very significant difference in the cutting technique that is applied to cutting wood as compared to aggregate. For wood, the cutting link of the cutting chain includes a forwardly projected cutting edge. This cutting edge is designed to penetrate into the wood material and develops a kerf by repeatedly gouging out particles of wood. For aggregate, the cutting link of the cutting chain includes a diamond impregnated flat face (the upper surface of a cutting block provided on the link) that rubs against the aggregate and develops a kerf by abrading away the aggregate.
For a wood cutting chain, it is not only desirable but essential that the leading edge of the cutting link be exposed and engage the wood being cut. The corresponding "face" of the wood cutting chain is relieved to avoid rubbing contact. For an aggregate cutting chain, it is desirable to provide a surface-to-surface rubbing contact (cutting block surface to aggregate kerf bottom). Exposing the leading edge of the cutting block serves no useful purpose and conversely should the leading edge impact a hard object imbedded in the aggregate, e.g. reinforcing rods or rebar, in concrete, the edge can become chipped. In a short time, the cutting efficiency will be undesirably reduced. Avoidance of such edge impact is desirable.
Providing guard portions on guard links of cutting chain are not uncommon for cutting chains used for cutting wood. However, they are used for protecting the depth gauge of the cutting link and not the cutter. Furthermore, the guard portion and the depth gauge are intentionally set below the peak (i.e., the cutting edge) of the cutter by a significant amount. The depth gauge is set, e.g. to a depth of 0.030 inch below the cutting edge and has to be periodically filed to maintain sufficient exposure of the cutting edge of the cutter. The guard portion is set below the depth gauge by an extent to provide sufficient exposure that will not interfere with the cutting operation throughout the life of the cutter. The concept of the depth gauge and/or guard portion as applied to wood cutting chain is not applicable to aggregate cutting chain where the material is abraded.
U.S. Pat. No. 4,920,947 directed to aggregate cutting chains provides side links preceding the cutting blocks with depth gauge portions on the side links that extend to the height of the cutting blocks and presumably protect the leading edge of the cutting block. However, the depth gauge portion that has been used is a hard steel that interferes with the cutting action of the cutting block. The hardness is necessary to achieve adequate wearability of the side links, i.e. the material surrounding the rivet holes and along the bottom edge that slides on the guide bar wears rapidly and a softer material would have inadequate life. Thus, if the hardness of the depth gauge of the '947 patent is maintained, the cutting action must be repeatedly stopped and the guard portions filed down below the cutting block height. A tedious procedure and one that is not acceptable.